Fix #2 and #5

From commit: bfbdf31

Fix for #2 - PyPI installation should properly install the lib's dependencies now

To address #5 - Optional 'state' and 'prompt' kwargs have been added to DiscordOAuthClient.redirect()

Some small housekeeping with example and test scripts.

Set discord.py dependency to <=1.7,<2 to prepare for discord.py 2.0 release possibly in the near future.